1. Field of the Invention
The present invention relates to drug-eluting medical devices; more particularly, this invention relates to systems, apparatus and methods for mounting to a delivery balloon a balloon-expandable stent, such as a polymeric stent.
2. Background of the Invention
FIGS. 1A and 1B depict perspective views of a prior art crimping station used to crimp a balloon expandable stent to a deployment balloon of a balloon catheter. The crimping station includes a crimper head 220, an interactive screen 216 for programming a crimping sequence, e.g., diameter reduction, dwell times between successive crimps, temperature control of the crimper jaws, etc. A carriage 242 aligns a catheter 209 with the opening 222 to the crimper head 220 and advances the distal end 209b of the catheter, where a stent 100 and the balloon are located, into the crimper head 220. The crimper head 220 includes three rollers 223, 224 and 225, which place a clean sheet of non-stick polymer material between the crimper jaws and stent 100 to avoid buildup of coating material on the jaws when plural stents having drug-polymer coatings are being crimped to balloon catheters.
FIG. 1B shows a perspective view of the carriage 242, which includes a slidable block 250 holding catheter 209. The block 250 is used to advance the catheter distal end 209b and stent 100 into and out of the crimper head 220 using knob 274. The catheter 209 is held within a groove 252 formed on the block 250. The catheter 209 shaft is retained in the groove 252 by a pair of cylindrical rods 253, 254 which are rotated down to trap the catheter shaft in the groove 252 before it is advanced into the crimper head 220 via the opening 222. The rods 253, 254 are rotated from the closed position (as shown) to an open position to allow the catheter 209 to be removed from the groove 252 by rotating hinge arms 253a, 254a clockwise (as indicated by A, B). A handle 255 is connected to the hinge arms 253a, 254a and rotated in direction C to move the hinge arms 253a, 254a to the open position. A rail 273 is connected to the block 250 at block extension 250a. The block 250 is displaceable over a distance “S”. An operator manually moves the distal end 209b and stent 100 towards or away from the crimper head 220 using the knob 274. The rail 273 is received within, and slides over a passage of a support 272, which is mounted to the table of the crimper station. The block 250 is received within, and slides along grooves (not shown) of a support piece 260. An abutment 275 of the support piece 260 serves as a stop to indicate when the catheter distal end 209b is positioned properly within the crimper head 220.
In operation, the operator manually places the catheter 209 within the groove 252 and holds it in place by rotating the handle clockwise to position the rods 253, 254 into the position shown in FIG. 1B. The operator then manually places the stent 100 over the balloon. Prior to inserting the distal end 209b within the crimper head 220, the operator must ensure that the stent is properly positioned on the balloon, i.e., the operator must ensure that the stent is located between marker bands of the balloon before placing the stent within the crimper head 220, so that when the balloon is inflated, the stent will expand properly within a patient's vasculature. the stent and balloon are then advanced into the crimper head by push the carriage forward until block 250 strikes or abuts the stop 275. When the block 250 hits the stop 275 the stent and balloon are in the desired position within the crimper head.
Preparing a stent-catheter assembly utilizing equipment such as that described above, and/or production techniques whereby operators dedicated to manually loading a stent on a balloon and ensuring the assembly is positioned/aligned properly so that the stent is properly crimped to the crimping head, is burdensome. In the case of high volume polymer stent-catheter assembly production there can be significantly more time spent properly crimping a polymer stent compared to a metal stent. Moreover, existing procedures for placing and aligning a stent, just prior to crimping has become more problematic and time-consuming as the lengths of deployment balloons have been shortened to about the length of a stent. Since the balloon length is matched more closely to the length of the stent (for purposes of avoiding damage to vascular tissue when the stent is deployed within a body) there is less margin for error by the operator. Given the small sizes for stents and balloons, great care must therefore be exercised by the operator to ensure that the stent is properly located on the balloon before crimping. If the stent is not properly positioned on the balloon before crimping, both the stent and catheter must the discarded.
The art recognizes a variety of factors that affect a polymeric stent's ability to retain its structural integrity when subjected to external loadings, such as crimping and balloon expansion forces. These interactions are complex and the mechanisms of action not fully understand. According to the art, characteristics differentiating a polymeric, bio-absorbable stent of the type expanded to a deployed state by plastic deformation from a similarly functioning metal stent are many and significant. These and related challenges faced in the manufacture and crimping of polymer stents to balloons are discussed in U.S. application Ser. Nos. 12/776,317 and 12/772,116.
One aspect of polymer stents, as compared to metal stents, that has presented certain challenges is the procedures required to ensure an acceptable yield when crimping large numbers of polymer stents to balloon catheters, as explained in more detail in applications U.S. application Ser. Nos. 12/776,317 and 12/772,116, as well as improving efficiency in crimping large numbers of polymer stents to balloons so that production-level polymer stent crimping does not impose unacceptable delays in the manufacturing process. The operation of crimping devices are time consuming when being used to crimp polymer stents and current production yields are less than favorable.
In view of the foregoing, there is a need to improve upon existing crimping processes, such as in the case of crimping polymer stents to balloon catheters.